Resistor unit and method of forming the same



Sept. 22, 1931. L. E. POWER 1,824,056

RESISTOR UNIT APID METHOD OF FORMING THE SAME Filed June 10, 1927Lmuranu E PUWQP v MW MW Patented Sept. 22, 1931 UNITED STATES PATENTOFFICE LAURENCE E. POWER, OF MILWAUKEE, WISCONSIN, ASSIGNOR, BY MESNEASSIGN- MENTS, 0F ONE-HALF T0 LYNDE BRADLEY AN D ONE-HALF TO HARRY L.BRADLEY,

BOTH OF MILWAUKEE, WISOONSIN RESISTOR UNIT AND METHOD OF FORMING THESAME Application filed June 10, 1927. Serial No. 197,882.

One difiiculty experienced in connection with resistor units when usedin circuits where it is of vital importance that their resistance valueremain constant, is that being of a more or less porous nature theyabsorb considerable moisture from the surrounding atmosphere as a resultof which their conductivity values vary according to the condition ofthe surrounding atmosphere and this invention has as an object theprovision of improved resistor units which are impervious to moisture tothus prevent changes in their conductivity values irrespective of thesurrounding atmospheric conditions.

Another object of this invention resides in the provision of an improvedmethod of forming resistor units whereby the units are renderedmoisture-proof to revent the entrance of the moisture in t e poresthereof.

It is a further object of this invention to provide an improved resistorunit of the character described having an outer wrapping or tube offibre or paper enclosing the exposed portions of the resistance materialto, with the end terminals or caps, completely enclose the resistancematerial and prevent its contact with the atmosphere.

With the above and other objects in view which will appear as thedescription pro ceeds, my invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the 'appended claims, itbeing understood that such changes in the precise embodiment of theherein disclosed invention may be made as come within the scope of theclaims.

In the accompanying drawings, I have illustrated several completeexamples of the physical embodiment of my invention constructedaccording to the best modes I have so far devised for the practicalapplication of the principles thereof, and in which:

Figure 1 is a view in side elevation and in perspective of theresistance body and the wrapping, therefor, respectively;

Figure 2 is a side view, partly in section and partly in elevation,illustrating one of the resistor units prior to the application of thelast end cap or terminal;

Figure 3 is a side view, with parts broken away, illustrating the firststep in subjecting the completed unit to a coating of paraflin or othermoisture-proofing material;

Figure 4 is a side view illustrating the manner of evacuating the airfrom the unit pores while the units are immersed in the water-proofingmaterial;

Figure 5 is a side view, with arts broken away, of a completed unit of as ightly modified construction, and

Figure 6 is a side view of a completed resistor unit with the endterminals or caps eliminated.

Referring now more particularly to the accompanying drawings, in whichlike numerals designate like parts throughout the several views, thenumeral 10 designates a bod of resistance material formed in accor ancewith my copending application Serial No. 197,881, or in any otherdesirable manner and adapted to have a constant resistance of apredetermined valve, end caps or terminals 11 of suitable design beingsecured over the ends of body 10 to provide means for connecting theunit in an electric circuit. The terminals 11 are preferably pressedover the ends of the body 10 after it has been formed and have apermanent fit thereon.

Due to the critical operation of radio receiver circuits in whichresistor units of this type are especially adapted. It is of utmostimportance that every possible safeguard be provided to preventvariations in the conductivity of the unit. The body 10 being of a moreor less porous nature has a tendency to absorb moisture, the eifect ofwhich is to change its conductivity and this objectionable feature isovercome by shielding all exposed surfaces of the unit from theatmosphere by the terminals 11 at its ends and a tube or wrapping 12 atits intermediate portion, the ends of the tube or wrapping having a snugengagement with the adjacent terminal whereby the resistance body isentirely enclosed.

I further protect the units from moisture by first immersing thecompleted units in a high grade parafiin or other water-proofingmaterial 13 having a high melting point of approximately 58 to 60degrees centigrade. The units are placed on a tray or other support 14and placed in a container 15 filled with paraflin which is melted byheat from a burner or other means 16. The container 15 with the unitstherein is then placed within a vessel 17 from which the air isevacuated through a tube 18, as a result of which the air within thepores of the units is extracted. The vacuum within the vessel 17 is thenreleased after a predetermined period of time and the melted parafiin orother water-proofing material enters the pores of the unit,v

thoroughly providing for the exclusion of moisture. The units are thenremoved from the'parafiin which congeals leaving a coating 19 thereon.

If desired, the end terminal members 11 may be dispensed with asdisclosed in my copending application, Serial No. 197,881, in which casethe ends 20 of the resistance unit are tapered to provide meansfacilitating engagement with a suitable mounting.

From the foregoing description taken in connection with the accompanyingdrawings, it will be readily apparent to those skilled in the art towhich an invention of the character described appertains that I providean improved resistor unit and method of forming the same whereby theunits are rendered substantially moistureproof.

What I claim as m invention is:

1. The hereindescri ed method of forming resistor units which consistsin molding a body of resistor material, in encasing the body, the endsof the casing terminating short of the ends of the unit, and in pressingterminal members on the ends of the body to bear against the ends of thecasing, the terminals and easing providing a substantiallyatmospherically tight enclosure for the unit to protect the same.

2. The hereindescribed method of forming resistor units which consistsin molding a bold of resistor material, in encasing the body, the endsof the casing terminating short of the ends of the unit, in pressingterminal members on the ends of the body to bear against the ends of thecasing, the terminals and casing providing a substantiallyatmospherically tight enclosure for the unit to protect the same, and incoating the assembled unit with a water proof material.

3. The hereindescribed method of forming resistor units which consistsin providing a body of resistance material, in encasing the body withthe ends of the easing terminating inwardly of the ends of the body, inpressing terminals on the ends of the' body to bear against the ends ofthe casing to enclose the body and protect the same against theatmosphere, and in coating the assembled unit with a waterproofingmaterial in an evacuated vessel.

4:- The hereindescribed method of forming resistor units which consistsin providing a body of resistance material, in encasing the body withthe ends of the casing terminating inwardly of the body, in pressingterminal members on the ends of the body to bear against the ends of thecasing to enclose the body and protect the same against the atmosphere,in immersing the assembled unit in molten paraflin, in placing the unitwhile immersed in parafiin in an evacuated vessel to open the pores ofthe casing, and in allowing air to enter the vessel to force theparafiin into the open pores of the casing to thoroughly impregnate thesame.

5. A' resistor unit, comprising a molded resistance body of uniformshape and dimensions throughout its length, an encasing member havinginternal dimensions and shape conforming with the shape of the moldedbody in transverse section and adapted to be engaged over-said body toenclose the intermediate portion thereof and havinga snug fit thereonwith its ends terminating short of the adjacent ends of said body, andterminal members having exterior dimensions approximating that of theencasing member and internal bores of shapes and dimensions to receivethe ends of the molded body with the inner marginal edges of theterminal members abutting the en s of the encasing member to, with theencasing member, provide an enclosing shield for the resistance body.

6. A resistor unit, comprising a molded resistance body of uniform shapeand dimensions throughout its length, an encasing member having internaldimensions and shape conforming with the shape of the molded body intransverse section and adapted to be engaged over said body to enclosethe intermediate portion thereof and having a snug fit thereon with itsends terminating short of the adjacent ends of said body, terminalmembers having exterior dimensions approximating that of the encasingmember and internal bores of shapes and dimensions to receive the endsof the molded body with the inner marginal edges of the terminal membersabutting the ends of the encasing member to, with the encasing member,provide an enclosing shield for the resistance body, and a coat ofwater-proof material for preventing leakage of moisture through theencasing member.

In testimony whereof I hereunto aflix my signature.

LAURENCE E. POWER.

